As the image shows, the content can not show correctly beacuse some content is covered by the submenu. If there are too many subMenus and it must be a new line for these submenu, these subMenus will cover the content.
This problem is more serious in IE6 because there are less menus for one line.
If we try to enlarge the browser, the mainmenu will not show correctly too if mainmenu need a new line. The mainmenu in a new line will be covered by submenu.
We can see in the last image, mainmenu “Goal” is been covered.
I think this problem will be more serious when user add many plugin which will add mainmenu or have many submenu.